1. Field of the Invention
The present invention relates to a process for producing 3-methyltetrahydrofuran. More particularly, it pertains to a process for producing 3-methyltetrahydrofuran which comprises distilling a mixed liquid containing 3-methyltetrahydrofuran and water and/or a specific alcohol as the principal components by adding an organic solvent to said mixed liquid to produce the objective 3-methyltetrahydrofuran substantially free from any of said alcohol and water.
2. Description of the Related Arts
3-Methyltetrahydrofuran is an extremely useful substance which is utilized as a comonomer for modifying poly(tetramethylene ether glycol) that is obtained by polymerizing tetrahydrofuran. (Refer to Japanese Patent Application Laid-Open No. 235320/1988 (Sho 63) and European Patent Application Laid-Open No. 343985.)
Various proposals have been made on the process for producing 3-methyltetrahydrofuran. For example, Japanese Patent Application Laid-Open No. 219981/1994 (Hei 6) describes the process for producing 2-methl-1,4-butanediol and 3-methyltetrahydrofuran by the hydrogenation of itaconic acid ester or 3-formyl-2-methylpropionic acid ester and also Japanese Patent Application Laid-Open No. 217768/1996 (Hei 8) describes the process for producing 3-methyltetrahydrofuran by the hydrogenation of methylsuccinic acid ester. However, when an attempt is made to produce 3-methyltetrahydrofuran by the use of the above-mentioned ester as a starting raw material, it is inevitable that the reaction product contains an alcohol as well as the objective 3-methyltetrahydrofuran. It is impossible to separate the 3-methyltetrahydrofuran from the alcohol by means of conventional distillation only, since it forms an azeotropic mixture with most of lower alcohols, for example, with methanol, forming an azeotrope having an azeotropic point of 64.5.degree. C. and an azeotropic composition consisting of 25% by weight of 3-methyltetrahydrofuran and 75% by weight of methanol.
In addition, Japanese Patent Publication Nos. 9464/1974, 38264/1974 and 1038/1975 each describe the process for producing 3-methyltetrahydrofuran by the hydrogenation of 2-methyl-butyrolactone. There is described, in J.Prakt.Chem 1972, 314(5-6), 840.,Ger.Offen.2236734, the process for producing 3-methyltetrahydrofuran by the cyclization dehydration reaction of 2-methyl-1,4-butanediol. However, when an attempt is made to produce 3-methyltetrahydrofuran by using the aforesaid starting raw material, it is inevitable that the reaction product contains water as well as the objevtive 3-methyltetrahydrofuran. It is impossible, as is the foregoing case, to separate the 3-methyltetrahydrofuran from the water by means of conventional distillation only, since it forms an azeotropic mixture with water, that is, an azeotrope having an azeotropic point of 75.8.degree. C. and an azeotropic composition consisting of 75% by weight of 3-methyltetrahydrofuran and 25% by weight of water.
On the other hand, consideration may be given to a process not in reliance on distillation, for example, a process in which the alcohol is washed away with water or a concentrated aqueous solution of caustic soda. However, the above-mentioned process can not be said to be efficient in separating the alcohol, since 3-methyltetrahydrofuran is inevitably lost to a certain extent by its being dissolved in the washing water and by the polymerization of itself.